The manner in which protein, phospholipid and pigment components are assembled into functional energy transducing membranes will be investigated in a bacterial model system. Results thus far in the facultatively photoheterotrophic bacterium Rhodopseudomonas sphaeroides indicate that pigment-polypeptide complexes are incorporated into the photosynthetic apparatus in the form of a precursor aggregate. Photochemical studies suggest that the precursor fraction is enriched in reaction center activity but that cyclic electron flow has not yet become established. Putative precursor polypeptides within the aggregate will be purified and characterized with respect to pulse-chase kinetics, amino acid composition, peptide maps, NH2-terminal sequence and immunological reactions and compared with the mature proteins. Pulse labeling will permit detection of transiently labeled polypeptides species within the membrane that undergo endoproteolytic processing during their incorporation. An in vitro system for the synthesis of photosynthetic membrane proteins will be established that will permit analysis of immediate translation products of their mRNAs. This system will be coupled to membrane vesicles from photosynthetically incompetent mutant strains. The restoration of light-dependent cyclic electron flow in the vesicles will provide a unique functional assay for a system coupling translation and insertion of membrane proteins. Sites of chromatophore phospholipid biosynthesis will be localized and the relation between phospholipid, pigment and protein synthesis in the assembly of the membrane will be elucidated with inhibitors and appropriate mutant strains. The proposed studies will aid in the elucidation of mechanisms involved in organelle assembly and provide a more complete understanding of this process at the molecular level.